LEDs are built on a substrate and are doped with impurities to create a p-n junction. A current flows from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Electrons and holes flow into the p-n junction from electrodes with different voltages. If an electron meets a hole, it falls into a lower energy level and releases energy in the form of a photon. The wavelength of the light emitted by the LED and the color of the light may depend on the band gap energy of the materials forming the p-n junction.
FIG. 1 is a cross-sectional side view of an embodiment of a p-side up lateral LED. The LED 100 has an n-type layer 103 disposed on the substrate 104. A multiple quantum well (MQW) 102 is disposed on the n-type layer 103 and the p-type layer 101 is disposed between the MQW 102 and a transparent-conductive layer (TCL) 113.
One or more p electrodes 121 are disposed on the TCL 113. Additionally, one or more n electrodes 106 are disposed on the n-type layer 103. This LED 100 may be mounted on a metal alloy in one instance. The p-type layer 101 and n-type layer 103 may be, for example, GaN. The MQW 104 may be GaInN or AlGaInP.
One shortcoming of this configuration is that the current preferably flows directly toward the n electrodes 106, as shown by arrows 109. This means that light is generated in areas within the LED which are blocked by the p electrodes 121. Electrodes, such as the p electrodes 121, may be fabricated of metal and this metal may not be an efficient transparent material for light. Therefore, most light generated in the MQW 102 beneath the p electrode 121 will be reflected and eventually absorbed inside the LED 100. This causes the input current versus light extraction ratio to be reduced, thereby reducing efficiency.
To overcome this shortcoming, a current blocking layer (CBL) may be used. The current blocking layer is disposed beneath the p electrode 121 to block current flow from the p electrode 121 to the p-type layer 101. FIG. 2A shows a first embodiment of a CBL 114. The CBL 114 is disposed above the p-type layer 101, and forces the current to spread to either side of the CBL 114, thereby reducing the amount of light that is generated directly beneath the p electrode. In some embodiments, the CBL 114 material is an insulating material such as SiO2, Si3N4 or undoped GaN. This material may be deposited on the surface of the LED 100, such as on the p-type layer 101, using a mask to allow deposition only in the desired location. In another embodiment, the insulating material is deposited on the entire surface of the p-type layer 101, and the unwanted material is then removed using a dry or wet etch process.
In another embodiment, shown in FIG. 2B, the CBL 114 is created by implanting ions 119 into the p-type layer 101 to create CBL 114. For example, argon or nitrogen may be implanted to create the non-conductive region represented by CBL 114. Typically, a mask 116 is used to only allow the ions 119 to be implanted in the region where the CBL 114 is desired.
The use of a CBL 114 maximizes the amount of light that is produced which ultimately will be emitted outside of the LED 100.
Unfortunately, the creation of the CBL 114 often requires additional process steps, which result in decreased throughout and increased cost. Therefore, it would be advantageous if the creation of the CBL 114 could be combined, or integrated with another process step to reduce manufacturing time and increase throughout.